1. Field of the Invention
This invention relates to chemically cross-linked poly(p-methylstyrene).
2. Description of the Prior Art
Styrene has been used for a long period of time in the manufacture of polymers and polystyrene has attained a large market for many purposes. Alkylated styrenes such as alpha-methylstyrene have also been of interest for certain purposes.
The nuclear alkyl substituted styrenes have also been used in various applications. The monomer which has been principally used is known as vinyltoluene. This is a mixture which consists mainly of meta- and para-methyl styrenes (vinyl toluenes) produced by the catalytic dehydrogenation of a mixture of the corresponding m- and p-ethyltoluenes. The ethyltoluene mixture is itself obtained by the fractional distillation of a mixture of the o-, m- and p-ethyltoluenes. The ratio of the m- and p-isomers in the monomer mixture is approximately 65:35 (m:p). A convenient summary of the preparation and properties of the monomer mixture and of polymers produced from it is given in "Styrene: Its Polymers, Copolymers and Derivatives" Ed. R. H. Boundy, R. F. Boyer, ACS Monograph Series, 1952, Hafner Publishing Company, pages 1232 to 1245.
In U.S. Pat. No. 3,008,937, there is disclosed cross-linking of m, p-vinyltoluene with a peroxide catalyst. It is to be noted, however, that the vinyltoluene used by and available to the patentees was that described in the aforementioned ACS Monograph. Such monomer mixture was manufactured by Dow Chemical Company, the patentees' assignee, and contained 65% meta-isomer and 35% para-isomer.
Chemically cross-linked poly-m, p-vinyltoluene is disadvantageous, because it has too low glass transition temperature (Tg). A Tg that is sufficiently high is an important factor in the end use of the cross-linked polymer as rigid food or beverage containers that are subjected to thermal conditions.